Electrode tissue reaction

Ideal material should be biologically inert, resistant to degradation over time, and not elicit a marked tissue reaction at the electrode-myocardium interface. Today, materials most often used for electrode building are platinum-iridium, pla-tinized-titanium-coated platinum, iridium oxide, and platinum. Carbon electrodes finally seem to be the least susceptible to corrosion. To increase their surface area, they can be treated with a process called activation, which roughens the lead surface. Carbon electrodes elicit only minimal tissue reac-... 

Obviously, fixation mechanisms and electrode-tissue interaction have crucial implications for lead extraction also. Encasement of the tines of a passive fixation lead by fibrous reaction may make transvenous lead removal more difficult than that of an active-fixation isodiametric leads. 

Contini C, Papi L, Pesola A et al (1973) Tissue reaction to intracavitary electrodes effect on duration and efficiency of unipolar pacing in patients with A-V block. J Cardio-vasc Surg (Torino) 14(3) 282-290... 

Radovsky AS, Van Vleet JF. Effects of dexamethasone elution on tissue reaction around stimulating electrodes of endocardial pacing lead in dogs. Am Heart J 1989 117 1288-1298. 

Johansson F, Wallman L, Danielson N, Schouenborg J, Kanje M (2009) Porous silicon as a potential electrode material in a nerve repair setting tissue reactions. Acta Biomater 5(6) 2230-2237 Khung Y-L, Graney SD, Voelcker NH (2006) Micropatteming of porous silicon films by direct laser writing. Biotechnol Prog 22(5) 1388-1393... 

The electrodes should not evoke undesirable biological responses, such as tissue reactions, antigenic reactions, and the like. For use in physiological systems, they must be able to operate within normal life-system pH ranges. The enzymes used must be able to withstand entrapment within a synthetic hydrophilic gel, copolymerization with other enzymes, or physical entrapment between membranes. 

As noted above, a key priority in electrode configuration and design is to provide safe communication between a specific location in ihe retina and the externally controlled electrical signals. Safe stimulation can be achieved with close proximity of the electrodes to the retinal tissue. This helps prevent irreversible reactions associated with high-stimulus charge density at the electrode/tissue interface. 

Preliminary work implanting the Utah array into human subjects used a pneumatic insertion device [37]. This short-term study showed variability in the tissue reaction to individual shanks in the array, and further work is required to correlate the histological findings with electrode function. 

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

Implantable microelectronic devices for neural prosthesis require stimulation electrodes to have minimal electrochemical damage to tissue or nerve from chronic stimulation. Since most electrochemical reactions at the stimulation electrode surface alter the hydrogen ion concentration, one can expect a stimulus-induced pH shift [17]. When translated into a biological environment, these pH shifts could potentially have detrimental effects on the surrounding neural tissue and implant function. Measuring depth and spatial profiles of pH changes is important for the development of neural prostheses and safe stimulation protocols. 

Although a number of reactions and events, that may contribute to the destruction of tissue, take place during the ECT treatment, it seems that water transport from the anode to cathode is the fundamental event, together with acidity changes associated with the electrode reactions at the anode and the cathode.25... 

The mechanisms of the necrosis of the cancer tissue by electrochemical treatment (ECT) are complex and not fully understood although the nature of several factors involved has been indicated. Nordenstrom pointed out the importance of electroosmosis, electrophoresis, electrode reactions, pH changes and the general drastic change in the microenvironment of the cancer tissue10,18 during ECT this and related work has been reviewed by Nilsson and coworkers.19... 

In order to explain all the salient features of the key experimental results on ECT (viz. listed as 1. to 6. at the beginning of Section II, Phenomenology of ECT), Vijh25 proposed a detailed electrochemical mechanism in which electroosmosis of the tissue (and thence water movement from anode to cathode) and electrode reactions (thence necrosis of the tissue, pH changes etc.) play the dominant roles. In particular, he presented a model and some quantitative considerations that delineate Nordenstrom s idea of electroosmosis through the narrow interstitial channels lined with fixed charges as the mechanism of the electrochemical destruction of the tumor tissue.10 Also he examined the role of electrode reactions and other events as possible contributory factors, as follows25 in Section III.2. 

A very thorough study on the effects of direct current on dog liver has been reported by Li et al.33 and their main findings have been summarized in the beginning of Section II, Phenomenology of ECT. This work brought out clearly the salient features of ECT such as changes in pH at the anode and the cathode, dehydration of the tissue at the anodic site and oedema at the cathodic site, and, the role of the electrode reactions etc. 

---